Researchers at McMaster University found a mechanism that explains why an infant's ability to respond to oxygen deprivation after birth is compromised by exposure to nicotine in the womb -- even in light to moderate amounts.

Lead author Josef Buttigieg and Dr. Alison Holloway said the laboratory research using rats explains how catecholamines -- a group of hormones released by the adrenal glands -- play a role in a baby's transition to the outside world.

During birth, the baby is exposed to low oxygen, which signals the adrenal glands to release the catecholamines, which contain adrenaline -- the "fight or flight" hormone -- said Buttigieg.

Catecholamines signal the baby's lungs to reabsorb fluid, to take its first breath, and help the heart beat more efficiently. For some months after birth, the adrenal gland still acts as an oxygen sensor, aiding in the baby's arousal and breathing responses.

However, the study said the ability to release catecholamines during these moments is impaired due to nicotine exposure and the infant becomes much more vulnerable to SIDS.

The study is published in the journal Federation of American Societies for Experimental Biology.